Good evening, with respect to a 300m 3.5l v6

I've already disassembled the valve rocker arms and bought a set of lifters to replace them, but I can't remove the old lifters. I've searched and the manuals I found say they need to be removed, but so far I haven't been able to remove them by pulling or pushing through the lubrication hole. Do they have some kind of locking mechanism or do I need a special tool?